Signaling growing interest in tunnels for a new light-rail line, Minneapolis Mayor R.T. Rybak sought assurances Tuesday that an underground route would not harm nearby lakes or prevent connecting the Southwest LRT to a future city streetcar line.

Rybak's stance was outlined in a letter to the Metropolitan Council, the agency overseeing the LRT project, as it nears a decision on whether to build tunnels in the Kenilworth corridor of Minneapolis or reroute conflicting freight traffic from the city to St. Louis Park.

Building one or more tunnels for LRT trains would eliminate the need to reroute the freight, which many St. Louis Park residents oppose, as well as satisfy some Minneapolis residents who don't want to see light-rail trains near their homes and parkland.

While Rybak said the Met Council should seriously consider a deep tunnel, he also left open the possibility of supporting shorter, shallow tunnels.

"I want to give Met Council the opportunity to demonstrate that is possible," he said in his letter to agency chair Susan Haigh.

Haigh called Rybak's comments "a positive sign that Minneapolis will continue its strong partnership on this project and that we can resolve the most challenging issue ... in a collaborative manner."

Rybak expressed concern over 1,000 feet separating the two shallow tunnels under consideration between Lake of the Isles and Cedar Lake. He indicated that Met Council engineers should look for ways to shorten the gap or use walls, fences or landscaping to hide the LRT trains when they run above ground and over a water channel linking the lakes.

Looking to contain costs

A 1.4-mile-deep tunnel in the Kenilworth corridor, an area popular with canoeists, bikers and runners, would cost up to $330 million to build. Rerouting the freight to St. Louis Park would cost an estimated $200 million. The shorter, shallow tunnels in Kenilworth could cost $160 million. An estimated $90 million in related costs would be added to any of the options.

Haigh said in a statement, "Our first priority is finding a way to contain costs on this project while also addressing community concerns and ensuring the rail line effectively serves as many riders as possible."

The mayor wrote that Met Council planners recently disclosed to the city "that there may be both temporary and permanent impacts on our lakes, with water being drained out of the tunnels and into the sewer system. … This is a very serious concern."

He said an assumption that "a shallow tunnel has a smaller long-term impact on the parkland and tree canopy than building LRT at grade … has not yet been demonstrated."

In an interview Tuesday, Rybak added, "We have to be rock solid certain this has no impact on the lakes."

Potential problems

One potential problem with the shallow tunnel under consideration is that it would end north of the planned West Lake Street LRT station, preventing a rail connection to a future streetcar line for the Midtown Greenway.

Rybak, in his letter, noted that the city, Hennepin County and the Met Council have been working to bring rail transit to the Greenway, where it could connect to the Hiawatha line.

Both Met Council tunnel options dropped a station planned for 21st Street in Minneapolis, a decision Rybak called "a big disappointment."

He came close in the interview to shutting the door on considering other routes for the Southwest LRT to avoid Kenilworth — including running it down the Midtown Greenway and north to downtown, an idea that was earlier considered and rejected.

"I think it's very difficult to consider realignments and it would have a serious negative impact on getting this built," he said. "We should never say 'never,' but I think another alignment at this point would slow down Southwest."

Earlier this week, Amazon announced that it's hiring 1,000 more full-time workers at its Shakopee fulfillment center. But city and county officials are still assessing reliable transportation options for the 1,500 people who already work there.